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perf_counter: fix the output lock

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Use -1 instead of 0 as unlocked, since 0 is a valid cpu number.

( This is not an issue right now but will be once we allow multiple
  counters to output to the same mmap area. )

[ Impact: prepare code for multi-counter profile output ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090505155437.232686598@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-05-05 17:50:25 +02:00 committed by Ingo Molnar
parent c5078f78b4
commit 22c1558e51
1 changed files with 4 additions and 3 deletions
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7
kernel/perf_counter.c
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@ -1409,6 +1409,7 @@ static int perf_mmap_data_alloc(struct perf_counter *counter, int nr_pages)
}
data->nr_pages = nr_pages;
atomic_set(&data->lock, -1);
rcu_assign_pointer(counter->data, data);
@ -1755,7 +1756,7 @@ static void perf_output_lock(struct perf_output_handle *handle)
if (in_nmi() && atomic_read(&data->lock) == cpu)
return;
while (atomic_cmpxchg(&data->lock, 0, cpu) != 0)
while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
cpu_relax();
handle->locked = 1;
@ -1784,7 +1785,7 @@ again:
* NMI can happen here, which means we can miss a done_head update.
*/
cpu = atomic_xchg(&data->lock, 0);
cpu = atomic_xchg(&data->lock, -1);
WARN_ON_ONCE(cpu != smp_processor_id());
/*
@ -1794,7 +1795,7 @@ again:
/*
* Since we had it locked, we can lock it again.
*/
while (atomic_cmpxchg(&data->lock, 0, cpu) != 0)
while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
cpu_relax();
goto again;